Internal combustion engines always comprise a cooling system for thermal management. The cooling system comprises a plurality of hydraulically interconnected conducts, which are comprised in the engine crankcase, engine cylinder block and engine cylinder head, to thereby defining an engine coolant circuit.
The engine coolant circuit is hydraulically connected to a coolant pump for circulating a coolant therein, such that the heat generated by engine components during normal operation is transferred by conduction and/or convection to the coolant. The engine coolant circuit is further hydraulically connected to a radiator for removing heat from the coolant. The coolant can be distilled water or preferably a mixture of water, antifreeze and other additives, which are suitable for increasing the cooling efficiency.
Some internal combustion engines, typically Diesel engines, comprise an exhaust gas recirculation (EGR) system, by means of which part of exhaust gas exiting the engine exhaust manifold is channeled back into the engine intake manifold, particularly for reducing NO emission. For achieving this result, the exhaust gas must be cooled before entering the engine intake manifold. The exhaust gas is conventionally cooled by means of one or more EGR coolers.
A so-called EGR cooler is constructed as a heat exchanger which is in hydraulic communication with the exhaust manifold and the intake manifold, such that the heat of exhaust gas is transferred by conduction and/or convection to a coolant which circulates in the heat ex-changer. In several realizations, the EGR cooler is comprised in an auxiliary cooling system, which is fully separated by the engine cooling sys-tem, and thereby comprises auxiliary radiator and auxiliary coolant pump. In other realizations, the EGR cooler is comprised in the engine cooling system, to thereby using a single radiator for both the engine coolant circuit and the EGR cooler, without any increased cost on the vehicle. A realization of the latter kind provides the cooling system which is described hereinafter.
As usual, the cooling system comprises an engine coolant circuit and a radiator. The radiator outlet communicates with the inlet of engine coolant circuit via a first pipeline, while the outlet of engine coolant circuit communicates with the radiator inlet via a second pipeline, to thereby closing the circuit. A coolant pump is located in the first pipeline, for moving the cool-ant towards the inlet of engine coolant circuit. The cooling system further comprises a bypass pipeline and a thermo-static valve. The bypass pipeline hydraulically connects the second pipeline directly to the first pipeline.
The thermostatic valve is located in the first pipeline, for closing the passageway when the coolant temperature in the engine is below a predetermined value, to thereby preventing the coolant to flow through the radiator. The thermostatic valve is useful for speeding up the engine warm-up and, during normal operation, for maintaining the coolant at a predetermined temperature.
Finally, the cooling system comprises an EGR cooler located in the bypass pipeline. When the thermostatic valve is open, part of the coolant from the engine coolant circuit is routed through the bypass pipeline, to there-by cooling the exhaust gas in the EGR cooler. Since the coolant in the engine coolant circuit can reach temperatures of about 95-100° C., it follows that the cooling system can not provide a strong EGR cooling.
By contrast, several tests have shown that a strong EGR cooling is useful for obtain low NOx emission. Moreover, when the thermostatic valve is closed in order to speed up the engine warm-up, the coolant does not flow through the radiator and it all flows through the EGR cooler, reaching in short time 95-100° C. Therefore, the cooling system can not perform the strong EGR cooling during the engine warm up. By contrast, it is generally very important to reduce the NO emission at the beginning of the emission cycle.
At least one aim of the present invention is to improve the described cooling system of the prior art, to thereby overcoming the above mentioned drawbacks. Another aim of the present invention is to meet the goal with a rather simple, rational and inexpensive solution. In addition, other aims, desirable features, and characteristics will become apparent from the subsequent summary and detailed description, and the appended claims, taken in conjunction with the accompanying drawings and this background.